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RAID stripe size performance

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February 29, 2004 5:15:53 PM

Hello all,
I read the RAID FAQ, but have additional questions.

I know that if the stripe size is not setup correctly then the RAID will be less effective. How much more less effective? Less effective than a single disk that is not in a RAID? Basically, if you choose the wrong stripe size, will it decrease performance BELOW THE LEVEL OF A SINGLE DRIVE that is not in a RAID?

My primary purpose on this RAID will be gaming and office applications, as well as watching DVDs and listening to music. The drives will be two WD740 Raptor 74gb drives on an Intel RAID controller on the motherboard (haven't bought motherboard yet).

I appreciate your time reading this,
-Chris
March 2, 2004 5:07:17 AM

It depends what you put on the drive.

For example, if you put your OS on a RAID0 drive with a 64K stripe you will lose performance over a single drive. This is because by far the majority of files in the OS are <20KB. If each stripe on the hard disk is 64KB then that means each 20KB file will sit in a 64KB block of its own on one hard disk. Effectively you are only reading the file from 1 hard disk and it is spaced out in 64KB blocks from the neighbouring files. This will increase seek times and decrease performance. If you have a 128KB file and use a 64KB stripe size your read time should be about the same. Basically the drives can read 2 64KB blocks from each drive simultaneously but there is am increased delay for each drive to find the file, so you get an improvement in read time, but a decrease in seek time which balances it out to average. As the files get larger so the advantages increase accordingly.

If you have a 16KB stripe size the advantages start increasing earlier, with a 32KB file you are already reading from 2 disks. But the problem is increased file fragmentation and hence read/write delays due to writing a large file into tiny pieces.

So there is no win/win situation. What you need to ask yourself is what is causing you the most performance delay. Usually it is writing out those big files, no one worries about how long it is taking to save a 4KB Word file, RAID can't help you there anyways. So if you are looking to improve the writing of 32MB .tiff files give your array a 64KB or 128KB stripe size. Saving of 4KB Word files won't be any faster, hell, it might even be a tad slower, but that's already so fast you won't even notice. But copying 100 32MB .tiff files or saving 1GB of streaming video will be a hell of alot easier.

<A HREF="http://www.anandtech.com/myanandtech.html?member=114979" target="_new">My PCs</A> :cool:
March 2, 2004 3:02:43 PM

Thank you for the informative post sjonnie!

Do you think RAID is even worth it then, if my primary applications will be games? Should I instead just run the drives normally and not in RAID? I have read that in video games, the only improvement is in loading levels and for the rest it is the same.

Maybe I'll just stick to a normal configuration instead of RAID 0.

Thanks for your time,
-Chris
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March 2, 2004 5:19:16 PM

What I did was creat 4 partitions on my drive, for the partition I was storing large files (like divX rips) I set the stripe size very high. For the OS I set it very low, and for the other 2 I set it to default. I dont think RAId is really worth it for playing games, then again if you have two drives there is no harm in RAIDing them.

[Insert witty comment here]
March 2, 2004 10:28:45 PM

128k is the fastest anyway you go

..this is very useful and helpful place for information...
March 2, 2004 11:13:54 PM

Thanks for the responses guys,

Blah, why do you say 128k is the fastest? Regardless of whether or not I choose to do RAID, would you all say I would notice a difference in read/write using the raptor drives? Also, I've never owned a 10,000rpm drive, what kind of cooling would you recommend? I have a Coolermaster case that has two 80mm fans blowing directly on the drives...is that sufficient?

Thanks so much,
-Chris
March 3, 2004 12:55:04 PM

I don't think RAID is worth it for an OS drive no. But then I'm not much of a gamer so I don't know how much it will help during games. Some say it helps, others not. I say check Perfmon and see if your harddrive is maxing out during your normal game play, if it is you could consider a RAID0 with a 16K block size or something.

<A HREF="http://www.anandtech.com/myanandtech.html?member=114979" target="_new">My PCs</A> :cool:
March 3, 2004 6:28:53 PM

as the fella above said, if the "primary purpose on this RAID will be gaming and office applications, as well as watching DVDs and listening to music." you need no RAID at all. 10k drive will be a .0003895433299203% faster, but the noise/heat level will be a 98750040305430222.4432% bigger.

..this is very useful and helpful place for information...
!